Check to see if there's any kind of oil on it's surface by sticking some masking tape down on that slick area. If the masking tape pulls up with less force than you'd normally expect, there's some sort of contamination of the surface.

Check to see where oil might drip off a ceiling fan. Or it could be that the convective currents that carry air upward over your stove end up causing cooking oil to converge on this spot.

If the tape pulls off easier than in other areas, I'd clean that area with paint thinner (aka: mineral spirits, varsol or "solvent") to eliminate what I expect is a cooking oil film.

(You can also use dish soap an water to clean up cooking oil, if that's what it is.)